Characterization of the dromedary milk casein micelle and study of its changes during acidification

Biochemical and physical properties of dromedary milk were studied at initi al pH and during an acidification with glucono-delta -lactone. In compariso n with bovine milk salt, citrate and nitrogen partition between soluble and micellar phases revealed several characteristics. Dromedary milk micelle p resented a more important mineral plus citrate charge (similar to 98 mg.g(- 1) casein). Micellar Mg, P and citrate proportions were higher, about 2/3, 2/3 and 1/3, respectively. During acidification, micellar mineral and citra te release started tardily (similar to pH 5.8) and the maximum of casein an d Pi solubilization took place at lower pH values, 4.9 and 4.8, respectivel y. Dromedary milk micelle seemed to maintain its integrity until about pH 5 .5, below, it underwent extensive biochemical and structural modifications mainly at pH 5.0. At this point, dromedary milk was characterized by a loos e microstructure, by a maximum of loss modulus and of micelle hydration and by a minimum of apparent viscosity. The pH 5.0 would be a transition pH be tween micellar structure and coagulum structure.